Will it be this piece of evidence that brings down Roz?

Did you watch Sunday night's episode 4?

Interesting developments in the ever-twisty world of Line of Duty...

After episode three's 'does this mean Nick's the murderer?!' ending, some considerable doubt has now been cast over the guilt of Roz's husband after we discovered he followed her to the scene on the night of Tim's murder because he believed she having an affair (explaining the police sighting of his car). Also, there was another CCTV sighting of Balaclava Man outside Nick's office, which doesn't really make sense if Nick is B.M - why would he have gone down the street in his killer gear given we know he was in the building when Steve fell, and when he meets Roz in the car he's back in his suit? Plus wouldn't police have discovered Nick's discarded outfit when they raided his office? As we pointed out last week, it did seem odd how quickly Nick managed to get changed out of a suit and tie into full killer garb in the time it took Steve to ride up the lift. Nevertheless - if Nick isn't Balaclava Man then what exactly was Balaclava Man doing hanging around his office stairwell?

One thing we love about Line of Duty is the show's ability to tip the balance of power so dramatically in a single scene. Case in point: the interrogation of Roz by Ted and Jamie. Just when you thought it was curtains for the increasingly desperate DCI, she turned the tables by attempting to discredit AC12, suggesting Ted was guilty of gender discrimination and Kate had coached a witness and planted evidence.

But Roz is not in the clear by a long chalk, and there's one thing in particular which we think could put DCI Huntley back in the firing line: her injured arm.

She was noticeably one-handed during the interrogation by Ted and Jamie, hiding her injured arm under the table, something that surely can't have gone unnoticed with an experienced investigator like Ted. Particularly since Ted himself suggested it was suspicious that Hana Reznikova didn't have any injuries consistent with the struggle that Roz claims she took part in at Tim's flat (there was also the thoughtful removal of Tim's fingers to clear evidence, which bore the hallmarks of a police pro).

Obviously Roz does have an injury consistent with the struggle, an injury that's now so infected she's been forced to go to hospital where the doctor has done a potentially incriminating swab. Will results from this swab, if AC12 can get hold of it, show up Tim's DNA? (I mean is that even possible? Notes on a postcard please, scientists) Either way, the arm damage - along with the anomaly in the re-examined blood swab - is arguably the biggest piece of incriminating evidence against Roz.

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Also, can we please talk about what happened in the last few moments of the episode? Why is the seemingly benign WPC Maneet Bindra doing secret alleyway folder-passing with ACC Hilton? Bindra joined AC12 in the previous season and has been a seemingly honest and dependable supporting character in this show (we particularly enjoyed her 'you're saying I look pregnant?' trick on Jamie). But has Bindra been a mole from the start? Is she the source of all Hilton's information on Ted that he passed to Roz? If so, what could be her motivation? She definitely didn't look happy about giving him the folder, which suggests he's got something on her. What that is we don't yet know.

Also, best exchange of the whole episode:

Jamie: 'Sorry Sir, I have to say it's Jamie not James'

Ted: 'Frankly son, right now I couldn't give a shit'

Roll on next Sunday!